Our temperatures warm significantly in the first half of March. We may have some chilly nights but all danger of frost has passed. Before setting out transplants and planting seeds of summer vegetables and flowering annuals, we need to prepare the soil at least two weeks ahead, especially when adding any sort of sterilized manure. Manure products, which should be sterilized to kill weed seeds and disease pathogens, contain urea which can act as excess nitrogen if not allowed to dissipate thoroughly before planting. Excess nitrogen can burn tender transplant roots.
With this year’s above average rainfall, the process of amending and turning the soil might be a little different.
Wet soil is not easy to work and amendments don’t mix in well. Pick up a handful of the soil in the planting bed and give it a squeeze. If the clump is too wet to hold together and your hand is covered with mud, the soil is too wet to work. Wait another week or two (of dry weather) to attempt to dig in amendments. When a clump of your soil holds its form when squeezed, you should be able to work in amendments.
Amendments improve soil texture, water retention, and add nutrients and beneficial micro organisms. New research show that plants growing in well-amended soil require less fertilizer and less water.
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To determine your soil type, dig a one foot hole and fill it with water. Time how long it takes the water to drain out of the hole. If it takes more than 20 minutes, you probably have clay soil or perhaps a layer of hardpan underneath the topsoil; if it takes less than five minutes you have really sandy soil. Your garden may have patches of both clay and sandy soils and hopefully a patch or two of sandy loam, the ideal soil.
Clay soil is amended with gypsum or gypsite to keep the clay molecules from binding together. Sandy soil is better able to hold water and nutrients when amended with compost or humus. A two-inch layer of organic compost or humus turned in twice a year will significantly improve soil quality within two years.
Other types of soil amendments are often recommended as miracle products. Some work well; some don’t . Recent research at UC Davis shows that biochar which is the end product of burning agricultural waste works to raise pH levels and improve soil texture. Our pH levels in the Fresno/Clovis area are high; we need to add sulfur which lowers pH levels. Also, adding biochar back into plantings of the original crop type gives better results-so amending the soil in almond orchards with biochar made from burned almond hulls has greater benefit. The research also shows that the micro organisms and beneficial bacteria contained in products sold as organic fertilizers and amendments often have a short shelf life. And that many micro organisms and beneficial fungi are picky about which plant’s roots they will attach to.
Try to find the freshest compost or humus, perhaps from your own compost pile. Experiment with amendments and brands, make notes, and continue to amend even healthy soil.
Note: check the soil around your drought-tolerant plants for excess moisture. Pull mulches away from overly wet root zones to allow the soil to dry.
Send Elinor Teague plant questions at firstname.lastname@example.org or email@example.com